System and method for transmitting a video signal from a transmitter to a receiver and reading and writing EDID

ABSTRACT

The present invention relates to system and method of reading and rewriting EDID in a video transmission system includes a transmitter transmitting a video signal and a receiver receiving the video signal that the transmitter transmitted which are connected to each other through digital interface, the method includes a reading step where the transmitter reads the EDID of the receiver through the digital interface; a first transmitting step where the transmitter transmit the video signal to the receiver on the basis of the EDID which the transmitter read; a second transmitting step where the receiver transmits a first message related to the EDID of the receiver; and a third transmitting step where the receiver transmits a second message related to the EDID of the receiver; wherein the transmitter, which received the first message from the receiver, does not read the EDID of the receiver until the second message is received.

CLAIM OF PRIORITY

This application is a continuation of application Ser. No. 12/931,022,filed on Dec. 4, 2009, now allowed, which claims the benefit of JapaneseApplication No. JP 2008-323878, filed Dec. 19, 2008, in the JapanesePatent Office, the disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an interface for transmitting a digitalvideo signal including an audio signal.

(2) Description of the Related Arts

Digital interfaces for transmitting a digital video signal, such as anHDMI (High Definition Multimedia Interface), a DVI (Digital VisualInterface), and a DisplayPort have been provided from the past.

These digital interfaces are used for transmitting a digital videosignal from a video transmitter to a video receiver. The videotransmitter is, for example, a digital recorder such as a DVD (DigitalVersatile Disc) reproducing device, a STB (Set Top Box), or a personalcomputer. The video receiver is, for example, a video display devicesuch as a monitor for a television or a personal computer.

In the case of connection through a digital interface such as the HDMI,a CP (Contents Protection, namely, copyright protection) technique suchas an HDCP (High-bandwidth digital Contents Protection) is employed, andtransmission and reception of a video signal is enabled only when thevideo transmitter and the video receiver are successfully authenticated.

However, a conventional authentication operation is executed while a HPDterminal is changed its level High to Low to High not only the time ofpower-on reset of the video receiver, but also every time when thedisplay switch to another input terminal or data related to thecharacteristics of the video receiver are rewritten. Accordingly, thevideo transmitter cannot read the data related to the characteristics ofthe video receiver until the data rewriting is completed, which leads toproblems that a video cannot be displayed or an interruption time of avideo is long.

Japanese Patent Application Laid-Open No. 2008-252819 describes anexample in which data related to the characteristics of a video receiverare rewritten in accordance with a state of the video receiver.

Japanese Patent Application Laid-Open No. 2006-246300 describes anexample of a display when authentication fails, but does not describeeliminating or shortening of a video interruption time caused byswitching of the input terminal or rewriting of data related to thecharacteristics of a video receiver

SUMMARY OF THE INVENTION

In view of the foregoing problems, the present invention provides a datareading method, and a video transmitter and a video receiver using thesame in which there is no video interruption time or a videointerruption time is short during switching of a display or datarewriting.

The present invention provides a video transmitter which transmits adigital video signal obtained by performing a contents protectionprocess to a video receiver through digital interfaces, wherein during aperiod when the video transmitter reads data related to thecharacteristics of the video receiver and transmits a digital videosignal generated on the basis of the read data by a default settingprocess to be executed at the time of power-on reset of the videoreceiver to the video receiver, when receiving a re-reading requestmessage for the data from the video receiver through a bidirectionalcommunication line incorporated into the digital interfaces, the datarelated to the characteristics of the video receiver are read and thevideo signal generated on the basis of the read setting data istransmitted to the video receiver.

According to the present invention, it is possible to provide a datareading method, and a video transmitter and a video receiver using thesame in which no interruption of a video occurs or a video interruptiontime is shorted due to no change in the signal level of the HPDterminal, even when data related to the characteristics of the videoreceiver are rewritten.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention;

FIG. 2 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention;

FIG. 3 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention;

FIG. 4 is a sequence diagram showing an example of operations of aconventional EDID rewriting process and a conventional CP authenticationprocess;

FIG. 5 is a sequence diagram showing an embodiment of an EDID readingprocessing operation according to the present invention;

FIG. 6 is a sequence diagram showing an embodiment of a CP process resetoperation according to the present invention

FIG. 7 is a sequence diagram showing an embodiment of an EDID readingprocessing operation and a CP process reset operation according to thepresent invention;

FIG. 8 is a diagram for comparing signal transmission methods for eachinterface according an embodiment of the present invention;

FIG. 9 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention;

FIG. 10 is a sequence diagram showing an embodiment of an EDID readingprocessing operation according to the present invention; and

FIGS. 11A to 11E are diagrams for explaining a message structureaccording to the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be notedthat constituent elements having common functions are given the samereference numerals in the respective drawings, and the explanationsthereof will be omitted as much as possible to avoid duplication of theexplanations.

[First Embodiment]

FIG. 1 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention, and the both are connected to each other through an HDMI. Thereference numeral 100 denotes a video transmitter which generates andtransmits a digital video signal, and 150 denotes a video receiver. Inthe video transmitter 100, the reference numeral 101 denotes a signalsource, 102 denotes an encryption unit, 103 denotes a video/audio signaltransmission unit, 104 denotes a CP processing unit, 105 denotes a CPU(Central Processing Unit), 106 denotes an EDID (Extended DisplayIdentification Data) reading unit, 107 denotes a detection unit, 108denotes a power source unit, 109 denotes a CEC (Consumer ElectronicsControl) unit, and 110 denotes a parameter storing unit. In addition, inthe video receiver 150, the reference numeral 151 denotes a displaypanel, 152 denotes a decryption unit, 153 denotes a video/audio signalreception unit, 154 denotes a CP processing unit, 155 denotes a CPU, 156denotes an EDID storing unit which stores the data of thecharacteristics of the receiver, 157 denotes a controlling unit, and 159denotes a CEC unit.

In FIG. 1, the video transmitter 100 is controlled by the CPU 105, andthe video receiver 150 is controlled by the CPU 155. Further, each ofthese CPUs 105 and 155 is operated by a user through an MMI (Man-MachineInterface) device including a remote controller (not shown) attached tothe video transmitter 100 or the video receiver 150.

Further, the video transmitter 100 and the video receiver 150 arecoupled to each other through an HDMI cable.

In the video transmitter 100, the signal source 101 is a video signalsource such as an external video input terminal, a DVD, or a broadcastreception unit, and outputs a video signal to the encryption unit 102.The encryption unit 102 encrypts (contents protection process) the inputvideo signal with, for example, an HDCP to be output to the video/audiosignal transmission unit 103. The video/audio signal transmission unit103 converts the input video signal into a serial transmission method ofa TMDS (Transmission Minimized Differential Signaling) method, andtransmits the resultant to the video/audio signal reception unit 153 ofthe video receiver 150 through a TMDS signal line.

At this time, the CP processing unit 104 performs authenticationregarding to whether or not the video receiver 150 that is theconnection target is provided with a legitimate HDCP processingfunction, through the CP processing unit 154 and a DDC (Display DataChannel) signal line. If authenticated, the CP processing unit 104outputs key information of encryption to the encryption unit 102.Specifically, the encryption unit 102 transmits a video signal obtainedby performing a contents protection process for the input video signalon the basis of the key information input from the CP processing unit104, and accordingly, the video receiver 150 cannot decrypt the videosignal without the key information by which the video signal obtained byperforming the contents protection can be decrypted.

It should be noted that as the TMDS method, a well-known techniquedescribed in, for example, Japanese Patent Application Laid-Open No.2007-28645 is used.

The power source unit 108 generates a DC voltage of +5V from an AC powersource (not shown) supplied to the video transmitter, and supplies thevoltage to the EDID storing unit 156 and the controlling unit 157 of thevideo receiver 150 through a +5V power source line.

The EDID reading unit 106 reads EDID from the EDID storing unit 156 ofthe video receiver 150 through the DDC signal line, and outputs thereceived EDID to the CPU 105. While the CPU 105 sets a format of a videosignal or an audio signal to be transmitted on the basis of the inputEDID to store the format setting parameter(a format information) intothe parameter storing unit 110, the CPU 105 gives an instruction on anoutput format of the video signal or the audio signal to the signalsource 101. Then, the CPU 105 controls the video/audio signaltransmission unit 103 not to transmit the video signal until theinitialization and the above-described CP process are completed.

In the case where the detection unit 107 detects a HPD (Hot Plug Detect)signal transmitted from the controlling unit 157 of the video receiver150 through a HPD signal line, the detection unit 107 outputs thedetected information of the HPD signal to the CPU 105.

The CEC unit 109 mutually transmits and receives a CEC control signalsuch as a remote control signal or a power-on/standby signal to/from theCEC unit 159 of the video receiver 150 through a CEC signal line.

In the video receiver 150, a video or audio signal transmitted from thevideo transmitter 100 is received by the video/audio signal receptionunit 153, and the signal is restored from the serial transmission methodto the video signal in the original format to be output to thedecryption unit 152. Further, the CP processing unit 154 outputs the keyinformation obtained through the authentication with the CP processingunit 104 of the video transmitter 100 to the decryption unit 152.

The decryption unit 152 performs a decryption process for the videosignal input from the video/audio signal reception unit 153 by using thekey information obtained from the CP processing unit 154, and outputsthe resultant to the display panel 151 on which the video is displayed.

The EDID storing unit 156 stores data representing the characteristicsof the video receiver 150, and the EDID is transmitted through the DDCsignal line in accordance with a reading operation of the EDID readingunit 106 of the video transmitter 100.

When the system is started, the controlling unit 157 transmits the HPDsignal as a trigger to the detection unit 107 of the video transmitter100.

The CEC unit 159 mutually transmits and receives the CEC control signalto/from the CEC unit 109 of the video transmitter 100 through the CECsignal line to control the timing of transmission and reception.

FIG. 9 is a block diagram showing the embodiment of configurations ofthe video transmitter and the video receiver according to the presentinvention. The reference numeral 911 denotes a DVD (Digital VersatileDisc), 912 denotes a D-VHS (Digital-Video Home System), 913 denotes anSTB (Set Top Box), 914 denotes an Audio Amp, 915 denotes a PVR (PersonalVideo Recorder), 951 denotes a television (hereinafter, referred to asTV), and 901 denotes HDMI cables.

In FIG. 9, the devices on the left side and the right side are the videotransmitter and the video receiver, respectively, which are connected toeach other through the HDMI cables 901. Further, for example, the DVD911 as a video transmitter can be coupled to the TV 951 as a videoreceiver through the HDMI cable 901, the Amp 914 and the HDMI cable 901.

Next, an EDID reading process of the present invention will be describedusing FIGS. 4 and 5. FIG. 4 is a sequence diagram showing an example ofoperations of a conventional EDID reading process and a conventional CPauthentication process. In addition, FIG. 5 is a sequence diagramshowing the embodiment of an EDID reading processing operation accordingto the present invention. In each case, the video transmitter and thevideo receiver are connected to each other through the HDMI.

In each of FIGS. 4 and 5, the video transmitter is represented as STBand the video receiver is represented as TV. Further, the HDMI cable isused for coupling the STB to the TV, and changes in the level of the HPDsignal in each sequence operation of the STB and the TV are shown on theright side. Further, in FIGS. 4 to 7, time passes from the top to thebottom of each drawing, and a time indicated on each horizontal line(dashed-dotted line) in the lateral axis direction is the same time.

As for the HPD signal level in each of FIGS. 4 and 7, “H” represents ahigh level (for example, 2.7V to 5.0V), and “L” represents a low level(for example, 0.0V to 0.4V).

In FIG. 4, a voltage of +5V is started to be supplied from the STB tothe TV through the +5V power source line at a time 401, and inputting ofthe power to the TV is started at a time 402. As a result, it isdetected that the HPD signal level is raised from “L” to “H” between atime 403 and a time 404 in the TV, and the HPD signal level becomes “H”at the time 404 in the STB.

When the HPD signal level is changed from “L” to “H”, the level changeof the HPD signal triggers reading of the EDID and CP authentication inthe STB. Specifically, in response to the result in which the “H” levelis detected, the STB starts to read the EDID at a time 405, and the TVtransmits the EDID at a time 406 in accordance with the readingoperation of the STB. After reading the EDID, the STB starts to performthe CP authentication for the TV at a time 407. The TV starts to performthe CP authentication process for the STB at a time 408. Specifically,the STB reads the EDID to set a video format to be output on the basisof the EDID, and performs the CP authentication process.

When the CP authentication process succeeds, the STB starts to transmitthe video signal to the TV (time 409). When the operation of the CPauthentication process is completed, the TV starts to receive the videosignal (starting of video/audio signal transmission) at a time 410.

As described above, in the case where it is determined by the TV torewrite the EDID at a time 411 in a state where the video signal istransmitted from the STB and is received by the TV, the HPD signal levelis switched from “H” to “L”. At a time 412, the TV starts to write newdata to the EDID storing unit 156 at a HPD signal level of “L”. Then, inthe case where the writing of data is completed at a time 413, the HPDsignal level is switched from “L” to “H”.

In the case where the HPD signal level is detected as “L” at the time412, the STB prohibits the reading of the EDID from the EDID storingunit 156. In the case where the HPD signal level is detected as “H” at atime 414, the level change triggers the STB to start to read the EDIDfrom the EDID storing unit 156 at a time 415.

The following sequence operations from a time 415 to a time 419 and atime 420 are the same as those from the time 405 to the time 409 and thetime 410, and thus, the explanations thereof will be omitted.

As described above, in the case where it is determined by the TV torewrite the EDID at the time 411, transmission of the video isinterrupted from, for example, the time 412 to the time 419, andreception of the video is interrupted from the time 411 to the time 420.

As described above by using FIG. 4, in the case where it is determinedby the TV to rewrite the EDID during transmission and reception of thevideo signal, it is necessary to interrupt the transmission andreception of the video signal in the conventional technique. Further,since the CP authentication process is performed, an interruption timeof a video becomes long. Thus, even in the case where it is determinedby the TV to rewrite the EDID during transmission and reception of thevideo signal, no interruption of a video occurs, or interruption time ofa video is shortened in the present invention, as the embodiment shownin the following FIGS. 5 to 7.

In FIG. 5, the processing operations from the time 401 when a powersource voltage of +5V is supplied to the time 410 when transmission andreception operations of the video signal are started (starting ofvideo/audio signal transmission) are the same as those in theconventional example of FIG. 4. Thus, the explanations thereof will beomitted and an explanation will be made from the process next to thetime 410.

For example, in the case where it is determined by the TV to rewrite theEDID at a time 501 during transmission and reception of the videosignal, the CPU 155 (see FIG. 1) transmits a message (controllingcommand) for prohibiting the reading of the EDID from the CEC unit 159to the CEC unit 109 of the STB through the CEC signal line. At thistime, the HPD signal is still at the “H” level.

The CEC unit 109 of the STB receives the message for prohibiting thereading of the EDID to be passed on to the CPU 105 at a time 502.Accordingly, the CPU 105 prohibits the EDID reading processingoperation.

In the case where the rewriting is completed, the TV transmits a readingrequest message (controlling command) for the EDID from the CEC unit 159to the CEC unit 109 of the STB through the CEC signal line at a time503. Accordingly, the CPU 105 can read the EDID. Specifically, the STBwhich received the reading request message for the EDID at a time 504allows the EDID reading unit 106 to start to read the EDID of the EDIDstoring unit 156 of the TV through the DDC signal line from a time 505.At this time, the HPD signal is still at the “H” level. It should benoted that the TV writes the EDID from the time 501 to the time 504.

The STB which reset the format or the like of an output video signal onthe basis of the read EDID starts to transmit the video/audio signalfrom the video/audio signal transmission unit 103 to the TV at a time507. At this time, the HPD signal is still at the “H” level.

As described above, the video in the format on the basis of the EDIDrewritten from the time 501 to the time 503 is displayed on the displaypanel 151 of the TV after a time 508.

According to the embodiment of FIGS. 1 and 5, in the video signaltransmission and reception system in which the video transmitter and thevideo receiver are coupled to each other by the HDMI method, defaultsetting of a video output format is performed on the basis of the EDIDwhen the power is supplied, and then, the CP authentication process isperformed, so that transmission and reception of the video signal isstarted. After transmission and reception of the video signal isstarted, a change in the level of the HPD signal is not used when it isnecessary to rewrite the EDID, but the messages (controlling commands)for prohibiting the reading of the EDID and for requesting to read theEDID which are communicated through the CEC signal line are used.Accordingly, it is possible to realize the video transmitter and thevideo receiver in which no interruption of a video occurs, the CPauthentication is not needed, and switching of the video/audio signal isfast even when the EDID is rewritten.

In the embodiment of FIG. 5, the STB adds a message for notifyinghandling information to the EDID reading prohibition message or the EDIDreading request message so as to ensure recognizing of a state in thevideo signal transmission and reception system including the STB and theTV, thus enhancing the reliability. For example, upon reception of amessage indicating that prohibition setting is completed for the EDIDreading prohibition message, rewriting of the EDID is started on the TVside. Accordingly, it is possible to avoid an abnormal operation inwhich the reading of the EDID is started by the STB when the EDIDreading prohibition message is not delivered to the STB due to somefalse operation. This is similarly applied to other embodiments of thepresent invention to be described later.

In the above-described embodiment, the HPD signal is used forinitialization only right after the power is supplied (or right afterinput switching) while being changed from Low to High. However, in casethe mechanism of the EDID reading prohibition or the EDID readingrequest by means of the message malfunctions, the HPD signal ispreferentially used when the HPD signal is changed to the low level, andthe operation performed by means of the message may be stopped.

Next, the CP authentication process of the present invention will bedescribed using FIG. 6. FIG. 6 is a sequence diagram showing theembodiment of a CP process reset operation of the present invention, andsignal processing is performed by the HDMI method shown in FIG. 1.

In FIG. 6, the processing operations from the time 401 when a DC powersource voltage of +5V is supplied to the time 410 when transmission andreception operations of the video signal are started are the same asthose in the conventional example of FIG. 4. Thus, the explanationsthereof will be omitted and an explanation will be made from the processnext to the time 410.

For example, in the case where it is determined by the TV that the CPprocess needs to be reset at a time 601 during transmission andreception of the video signal, the CEC unit 159 outputs a CP reset andauthentication starting message to the CEC signal line under control ofthe CPU 155 (see FIG. 1) of the TV. The CEC unit 109 of the STB receivesthe same message to be passed on to the CPU 105. At this time, the HPDsignal is still at the “H” level.

After the CEC unit 109 receives the CP reset and authentication startingmessage at a time 602, the CPU 105 of the STB instructs the CPprocessing unit 104 of the STB to start the CP authentication with theTV. From a time 603, the CP processing unit 104 of the STB and the CPUprocessing unit 154 of the TV start the CP authentication process. TheCP processing unit 104 outputs key information obtained as a result ofthe CP authentication process to the encryption unit 102. From a time605, the video/audio signal transmission unit 103 starts to transmit thevideo signal encrypted by the encryption unit 102 on the basis of thekey information to the TV through the TMDS signal line. The video/audiosignal reception unit 153 of the TV receives the encrypted video signalto be passed on to the decryption unit 152 of the TV. From a time 606,the decryption unit 152 decrypts the input video signal on the basis ofthe key information supplied from the CP processing unit 154 to bedisplayed on the display panel 151. At this time, the HPD signal isstill at the “H” level.

According to the embodiment of FIG. 6, in the video signal transmissionand reception system in which the video transmitter and the videoreceiver are coupled to each other by the HDMI method, default settingof a video output format is performed on the basis of the EDID when thepower is supplied, and then the CP authentication process is performed,so that the video interfaces are initialized. After transmission andreception of the video signal is started, a change in the level of theHPD signal is not used as a reset signal for the CP process, but the CPreset and authentication starting message (controlling command) which iscommunicated through the CEC signal line is used. Accordingly, it ispossible to realize the video transmitter and the video receiver inwhich switching of the video/audio signal is fast because even when theCP process is reset, the reading operation of the EDID is not necessaryand an interruption time of a video can be shortened.

Next, there will be described a case, using FIG. 7, in which both of theEDID reading process and the CP process reset operation of the presentinvention are performed. FIG. 7 is a sequence diagram showing theembodiment of the EDID reading process and the CP process resetoperation of the present invention, and signal processing is performedby the HDMI method shown in FIG. 1.

In FIG. 7, the processing operations from the time 401 when a DC powersource voltage of +5V is supplied to the time 410 when transmission andreception operations of the video signal are started are the same asthose in the conventional example of FIG. 4. Thus, the explanationsthereof will be omitted and an explanation will be made from the processnext to the time 410.

For example, in the case where it is determined by the TV to rewrite theEDID and to reset the CP process at a time 701 during transmission andreception of the video signal, the CPU 155 (see FIG. 1) transmits amessage for prohibiting the reading of the EDID from the CEC unit 159 tothe CEC unit 109 of the STB through the CEC signal line. The CPU 105 ofthe STB which received the message of prohibiting the reading of theEDID at a time 702 controls so as not to perform the reading of the EDIDuntil the EDID reading request message is received.

From a time 701, the TV starts to rewrite the EDID of the EDID storingunit 156 and the rewriting is completed at a time 703. When therewriting is completed, the CPU 155 transmits an EDID reading requestand CP process reset message from the CEC unit 159 to the CPU 105through the CEC unit 109 of the STB. At this time, the HPD signal isstill at the “H” level. Thus, the message for prohibiting the reading ofthe EDID is used for triggering data rewriting.

The CPU 105 of the STB which received the EDID reading request and CPprocess reset message at a time 704 requests the EDID storing unit 156of the TV to read the EDID at a time 705. The EDID storing unit 156starts to transmit the EDID at a time 706. Next, at a time 707 when theSTB completes the reading of the EDID, the CP processing unit 104 of theSTB transmits a CP process starting message to start the CPauthentication process with the CP processing unit 154 of the TV.

Upon reception of the CP process starting message from the STB, the CPprocessing unit 154 of the TV performs the CP authentication with the CPprocessing unit 104 of the STB at a time 708, and the video isinterrupted during the CP authentication process (from a time 707 to atime 709). However, at this time, the HPD signal is still at the “H”level.

When the CP processing unit of the STB completes the CP authentication,the STB starts to transmit the video signal on the basis of therewritten EDID and the CP authentication from the video/audio signaltransmission unit 103 to the video/audio signal reception unit 153 ofthe TV at a time 709. The TV receives the video signal on the basis of anew result of CP authentication and the EDID transmitted from the STB,so that the received video signal is decrypted and displayed on thebasis of the new CP authentication at a time 710. At this time, the HPDsignal is still at the “H” level.

According to the embodiment of FIG. 7, in the video signal transmissionand reception system in which the video transmitter and the videoreceiver are coupled to each other by the HDMI method, default settingof a video output format is performed on the basis of the EDID when thepower is supplied, and then the CP authentication process is performed,so that the video interfaces are initialized. After transmission andreception of the video signal is started, a change in the level of theHPD signal is not used as a trigger signal for rewriting the EDID, butthe message (controlling command) for prohibiting the reading of theEDID which is communicated through the CEC signal line is used.Accordingly, it is possible to realize the video transmitter and thevideo receiver in which an interruption time of a video is short evenwhen the EDID is rewritten and the CP process is reset aftertransmission and reception of the video signal is started.

It should be noted that if items of the embodiment of FIGS. 5 to 7 arereplaced by those shown in a comparison table of FIG. 8, to be describedlater, in FIG. 2 (second embodiment) and FIG. 3 (third embodiment) to bedescribed later, the embodiment can be similarly conducted even in a DVImethod and a DisplayPort method.

FIG. 10 is a sequence diagram showing the embodiment of an EDID readingprocessing operation of the present invention. In the embodiment of FIG.5, the CEC unit 159 of the TV transmits the message for prohibiting thereading of the EDID only when writing is started, and transmits the EDIDreading request message after completion of writing. In addition, theSTB prohibits the reading of the EDID when the STB receives one messagefor prohibiting the reading of the EDID, and prohibits the reading ofthe EDID until the STB receives the EDID reading request message.However, in the embodiment of FIG. 10, the message for prohibiting thereading of the EDID may be transmitted to the STB at predetermined timeintervals (cycles), for example, intervals of 400 ms (times 1001, 1003,and 1005) during a period of rewriting the EDID in the EDID storing unit156, and the reading of the EDID may be prohibited every time the STBreceives the message during a predetermined period longer than thepredetermined cycle, for example, up to 500 ms after reception of themessage.

In this case, the TV transmits the message for prohibiting the readingof the EDID at the predetermined intervals from the time (a time 1001)rewriting of the EDID in the EDID storing unit 156 is started, and doesnot transmit the same after completion of the rewriting (a time 1007).Thus, the TV may be operated on the assumption that the reading requestmessage is received 500 ms later from the reception of the last messagefor prohibiting the reading of the EDID.

An example of a structure of the message described above is shown inFIGS. 11A to 11E. Each message includes a Header 811, an Op Code 812, anOp Data 813 related to a destination Physical Address, and an OP Data814 (824, 834, or 844) representing reading prohibition.

FIG. 11A represents a message for showing EDID reading prohibition, FIG.11B represents a message for showing an EDID reading request, FIG. 11Crepresents a message for showing CP reset and starting ofauthentication, and FIG. 11D represents a message for showing an EDIDreading request and CP authentication initialization. Each message hasone Op Data other than the Physical Address. However, in order to reducea message frequency, in FIG. 11E, it is advantageous in enhancing theusage efficiency of a low-speed communication line if the EDID readingprohibition Op Data and two pieces of OP Data representing the EDIDreading and the CP authentication initialization are carried by onemessage. The EDID reading prohibition Op Data and two pieces of Op Datarepresenting the EDID reading and the CP authentication initializationmay be collectively defined as one piece of Op Data.

At this time, it is preferable that a time period from the EDID readingprohibition to the EDID reading is set to 100 ms or longer from theviewpoint of compatibility with a conventional HDMI device with HDCP.Further, it is desirable that the time period is set to less than 500 msbecause a long time period leads to delay of response.

According to the present invention, it is possible to always set the HPDsignal at the “H” level. Thus, the embodiment may be applied to a casein which a HPD terminal is considered to be always at the high levelexcept for the time right after power supplying and another signal istransmitted to the HPD terminal.

[Second Embodiment]

FIG. 2 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention, and the both are configured by interfaces of a DVI method.The reference numeral 200 denotes a video transmitter which generatesand transmits a digital video signal, and 250 denotes a video receiver.In the video transmitter 200, the reference numeral 201 denotes a signalsource, 202 denotes an encryption unit, 203 denotes a video signaltransmission unit, 204 denotes a CP processing unit, 205 denotes a CPU,206 denotes an EDID reading unit, 207 denotes a detection unit, 208denotes a power source unit, and 210 denotes a parameter storing unit.In addition, in the video receiver 250, the reference numeral 251denotes a display panel, 252 denotes a decryption unit, 253 denotes avideo signal reception unit, 254 denotes a CP processing unit, 255denotes a CPU, 256 denotes an EDID storing unit, and 257 denotes acontrolling unit.

In FIG. 2, the video transmitter 200 is controlled by the CPU 205, andthe video receiver 250 is controlled by the CPU 255. Further, each ofthese CPUs 205 and 255 is operated by a user through an MMI deviceincluding a remote controller (not shown) attached to the videotransmitter 200 or the video receiver 250.

Further, the video transmitter 200 and the video receiver 250 arecoupled to each other through a DVI cable.

In the video transmitter 200, the signal source 201 is a video signalsource, and outputs a video signal to the encryption unit 202. Theencryption unit 202 encrypts the input video signal with, for example,an HDCP to be output to the video signal transmission unit 203. Thevideo signal transmission unit 203 converts the input video signal intoa serial transmission method of a TMDS method, and transmits theresultant to the video signal reception unit 253 of the video receiver250 through a TMDS signal line.

At this time, the CP processing unit 204 performs authentication withthe CP processing unit 254 regarding to whether or not the videoreceiver 250 that is the connection target is provided with a legitimateHDCP processing function, through a DDC signal line. If authenticated,the CP processing unit 204 outputs key information of encryption to theencryption unit 202. Specifically, the encryption unit 202 transmits avideo signal obtained by performing a contents protection process forthe input video signal on the basis of the key information input fromthe CP processing unit 204, and accordingly, the video receiver 250cannot decrypt the video signal without the key information by which thecopy protection signal can be decrypted.

The power source unit 208 generates a DC power source voltage of +5Vfrom an AC power source (not shown) supplied to the video transmitter,and supplies the voltage to the EDID storing unit 256 and thecontrolling unit 257 of the video receiver 250 through a +5V powersource line.

The EDID reading unit 206 reads EDID from the EDID storing unit 256 ofthe video receiver 250 through the DDC signal line, and outputs thereceived EDID to the CPU 205. While the CPU 205 sets a format of a videosignal to be transmitted on the basis of the input EDID to store theformat information into the parameter storing unit 210, the CPU 205gives an instruction on an output format of the video signal to thesignal source 201. Then, the CPU 205 controls the video signaltransmission unit 203 not to transmit the video signal until theinitialization and the above-described CP process are completed.

In the case where the detection unit 207 detects a HPD signaltransmitted from the controlling unit of the video receiver 250 througha HPD signal line, the detection unit 207 outputs the detectedinformation of the HPD signal to the CPU 205.

In the video receiver 250, a video signal transmitted from the videotransmitter 200 is received by the video signal reception unit 253, andthe signal is restored from the serial transmission method to the videosignal in the original format to be output to the decryption unit 252.Further, the CP processing unit 254 performs authentication with the CPprocessing unit 254 regarding to whether or not the video transmitter200 that is the connection target is provided with a legitimate HDCPprocessing function, through the DDC signal line. If authenticated, theCP processing unit 254 outputs key information of encryption to thedecryption unit 252. Specifically, the decryption unit 252 performs adecryption process for the input video signal on the basis of the keyinformation input from the CP processing unit 254, and outputs theresultant to the display panel 251 on which the video is displayed.

As described above, in the case where the information signal capable ofdecrypting the video signal obtained by performing a contents protectionprocess is input, the decryption unit 252 decrypts the input videosignal to be output to the display panel 251 on which the video isdisplayed.

The EDID storing unit 256 stores data representing the characteristicsof the video receiver 250, and the EDID is transmitted through the DDCsignal line in accordance with a reading operation of the EDID readingunit 206 of the video transmitter 200.

When the system is started, the controlling unit 257 transmits the HPDsignal as a trigger to the detection unit 207 of the video transmitter200.

[Third Embodiment]

FIG. 3 is a block diagram showing an embodiment of configurations of avideo transmitter and a video receiver according to the presentinvention, and the both are configured by interfaces of a DisplayPortmethod. The reference numeral 300 denotes a video transmitter whichgenerates and transmits a digital video signal, and 350 denotes a videoreceiver. In the video transmitter 300, the reference numeral 301denotes a signal source, 302 denotes an encryption unit, 303 denotes avideo/audio signal transmission unit, 304 denotes a CP processing unit,305 denotes a CPU, 309 denotes an AUX-CH (Auxiliary-Channel) unit, 307denotes a detection unit, 308 denotes a power source unit, and 310denotes a parameter storing unit. In addition, in the video receiver350, the reference numeral 351 denotes a display panel, 352 denotes adecryption unit, 353 denotes a video/audio signal reception unit, 354denotes a CP processing unit, 355 denotes a CPU, 359 denotes an AUX-CHunit, 356 denotes an EDID storing unit, and 357 denotes a controllingunit.

In FIG. 3, the video transmitter 300 is controlled by the CPU 305, andthe video receiver 350 is controlled by the CPU 255. Further, each ofthese CPUs 305 and 355 is operated by a user through an MMI deviceincluding a remote controller (not shown) attached to the videotransmitter 300 or the video receiver 350.

Further, the video transmitter 300 and the video receiver 350 arecoupled to each other through a DisplayPort cable.

Communications between the CP processing unit 304 of the videotransmitter 300 and the CP processing unit 354 of the video receiver 350and communications between the CPU 305 of the video transmitter 300 andthe EDID storing unit 356 of the video receiver 350 are performedthrough the AUX-CH unit 309 and the AUX-CH unit 359 which are coupled toeach other through an AUX-CH signal line.

In the video transmitter 300, the signal source 301 is a video signalsource, and outputs a video signal to the encryption unit 302. Theencryption unit 302 encrypts the input video signal with, for example,an HDCP or a DPCP (DisplayPort Contents Protection) to be output to thevideo/audio signal transmission unit 303. The video/audio signaltransmission unit 303 converts the input video signal into a serialtransmission method of a Main Link method, and transmits the resultantto the video/audio signal reception unit 353 of the video receiver 350through a Main Link signal line.

At this time, the CP processing unit 304 performs authentication withthe CP processing unit 354 regarding to whether or not the videoreceiver 350 that is the connection target is provided with a legitimateHDCP processing function, through the AUX-CH signal line. Ifauthenticated, the CP processing unit 304 outputs key information ofencryption to the encryption unit 302. Specifically, the encryption unit302 transmits a video signal obtained by performing a contentsprotection process for the input video signal on the basis of the keyinformation input from the CP processing unit 304, and accordingly, thevideo receiver 350 cannot decrypt the video signal without the keyinformation by which the copy protection signal can be decrypted.

The power source unit 308 generates a DC power source voltage of +3.3Vfrom an AC power source (not shown) supplied to the video transmitter,and supplies the voltage to the controlling unit 357 of the videoreceiver 350 through a +3.3V power source line.

While the CPU 305 sets a format of a signal on the basis of the EDIDtransmitted from the EDID storing unit 356 of the video receiver 350 tostore the format information into the parameter storing unit 310, theCPU 305 gives an instruction on an output format of the video signal tothe signal source 301. Then, the CPU 305 controls the video/audio signaltransmission unit 303 not to transmit the video signal until theinitialization and the above-described CP process are completed.

In the case where the detection unit 307 detects a HPD signaltransmitted from the controlling unit of the video receiver 350 througha HPD signal line, the detection unit 307 outputs the detectedinformation of the HPD signal to the CPU 305.

In the video receiver 350, a video signal transmitted from the videotransmitter 300 is received by the video/audio signal reception unit353, and the signal is restored from the serial transmission method tothe video signal in the original format to be output to the decryptionunit 352. Further, the CP processing unit 354 performs authenticationwith the CP processing unit 354 regarding to whether or not the videoreceiver 350 that is the connection target is provided with a legitimateHDCP processing function, through the AUX-CH signal line. Ifauthenticated, the CP processing unit 354 outputs key information ofencryption to the encryption unit 302. Specifically, the encryption unit302 transmits and outputs the video signal obtained by performing acontents protection process on the basis of the key information inputfrom the CP processing unit 304.

As described above, in the case where the information signal capable ofdecrypting the video signal obtained by performing a contents protectionprocess is input, the decryption unit 352 decrypts the input videosignal to be output to the display panel 351 on which the video isdisplayed.

The EDID storing unit 356 stores data representing the characteristicsof the video receiver 350, and the EDID is transmitted to the CPU 305 ofthe video transmitter 300 through the AUX-CH unit 359, AUX-CH signalline, and the AUX-CH unit 309.

When the system is started, the controlling unit 357 transmits the HPDsignal as a trigger to the detection unit 307 of the video transmitter300.

The types of signals in the respective interface methods in the first tothird embodiments will be collectively described using FIG. 8. FIG. 8 isa diagram for comparing each embodiment of the signal transmissionmethod for each interface of the present invention.

In FIG. 8, for three types of connection interfaces (HDMI, DVI, andDisplayPort), (1) shows a video/audio transmission method, (2) shows acommunication method of EDID reading/CP authentication, (3) shows atrigger method of EDID reading/CP authentication, (4) shows a low-speedbidirectional communication method, (5) shows a CP method, and (6) showsa trigger method used for the present invention which is alternative toan “H”/“L” switching method of a conventional HPD during transmissionand reception of a video signal.

As will be apparent from FIG. 8, according to the first to thirdembodiments, in the video signal transmission and reception system inwhich the video transmitter and the video receiver are coupled to eachother by anyone of the HDMI method, the DVI method, and the DisplayPortmethod, default setting of a video output format is performed on thebasis of the EDID when the power is supplied, and then, the CPauthentication process is performed, so that the video interfaces areinitialized. Accordingly, it is possible to realize the data readingmethod, and the video transmitter and the video receiver in which aftertransmission and reception of the video signal is started, nointerruption of a video occurs or an interruption time is short.

What is claimed is:
 1. A video transmitting system, in which atransmitter device to transmit a video signal and a receiver device toreceive the video signal transmitted by the transmitter device areconnected through a digital interface including an HPD (Hot Plug Detect)line, the digital interface having a CEC (Consumer Electronics Control)interface to transmit CEC messages including a Header and an Op Code,wherein the receiver device includes an EDID (Extended DisplayIdentification Data) recording part to record an EDID indicating theperformance of the receiver device, wherein: the transmitter devicereads the EDID of the receiver device through the digital interface, andtransmits the video signal to the receiver device based on the read EDIDof the receiver device, the receiver device transmits a first CECmessage for prohibiting the transmitter device to read the EDID of thereceiver device and resetting a contents protection while a signal levelof the HPD line is a high level, and transmits a second CEC message forenabling the transmitter device to read the EDID of the receiver devicewhile a signal level of the HPD line is a high level, the transmitterdevice transmits a reply for the first CEC message to the receiverdevice, transmits a reply for the second CEC message to the receiverdevice and is prohibited to read the EDID of the receiver device afterthe transmitter device receives the first CEC message from the receiverdevice, until the transmitter device receives the second CEC messagefrom the receiver device, and the transmitter device starts a process ofthe contents protection after the transmitter device receives the secondCEC message from the receiver device.
 2. A method of reading an EDID(Extended Display Identification Data) in a video transmitting system inwhich a transmitter device to transmit a video signal and a receiverdevice to receive the video signal transmitted by the transmitter deviceare connected through a digital interface including an HPD (Hot PlugDetect) line, the digital interface having a CEC (Consumer ElectronicsControl) interface to transmit CEC messages including a Header and an OpCode, the method comprising the steps of: reading, by the transmitterdevice, the EDID of the receiver device through the digital interface:transmitting, by the transmitter device, the video signal to thereceiver device based on the read EDID of the receiver device: wherein:the receiver device transmits a first CEC message for prohibiting thetransmitter device to read the EDID of the receiver device and resettinga contents protection while a signal level of the HPD line is a highlevel, and transmits a second CEC message for enabling the transmitterdevice to read the EDID of the receiver device while a signal level ofthe HPD line is a high level, the transmitter device transmits a replyfor the first CEC message to the receiver device, transmits a reply forthe second CEC message to the receiver device and is prohibited to readthe EDID of the receiver device after the transmitter device receivesthe first CEC message, until the transmitter device receives the secondCEC message from the receiver device, and the transmitter device startsa process of the contents protection after the transmitter devicereceives the second CEC message from the receiver device.
 3. A videotransmitting system, in which a transmitter device to transmit a videosignal and a receiver device to receive the video signal transmitted bythe transmitter device are connected through a digital interface,wherein the digital interface has a CEC (Consumer Electronics Control)line to transmit CEC messages including a Header and an Op Code and anHPD (Hot Plug Detect) line, wherein: the receiver includes an EDID(Extended Display Identification Data) recording part to record an EDIDindicating a performance of the receiver device, the transmitter devicereads the EDID of the receiver device through the digital interface,determines a format of the video signal to be transmitted based on theread EDID of the receiver device, and transmits the video signal to thereceiver device by the determined format, the receiver device transmitsa first CEC message for prohibiting the transmitter device to read theEDID in a case where the receiver device lets the transmitter devicereset a contents protection process while a signal level of the HPD lineis a high level, and thereafter, the receiver device transmits a secondCEC message, to the transmitting device, for enabling the transmitterdevice to start a process of the contents protection while a signallevel of the HPD line is a high level, the transmitter device does notread the EDID of the receiver device after the transmitter devicereceives the first CEC message, until the transmitter device receivesthe second CEC message from the receiver device, and the transmitterdevice starts the process of the contents protection after thetransmitter device receives the second CEC message from the receiverdevice.
 4. A method of reading an EDID (Extended Display IdentificationData) in a video transmitting system in which a transmitter device totransmit a video signal and a receiver device to receive the videosignal transmitted by the transmitter device are connected through adigital interface, wherein the digital interface having a CEC (ConsumerElectronics Control) line to transmit CEC messages including a Headerand an Op Code and an HPD (Hot Plug Detect) line, the method comprisingthe steps of: reading, by the transmitter device, the EDID of thereceiver device through the digital interface, determining, by thetransmitter device, a format of the video signal to be transmitted basedon the read EDID of the receiver device, and transmitting the videosignal to the receiver device by the determined format, transmitting, bythe receiver device, a first CEC message for prohibiting the transmitterdevice to read the EDID of the receiver device in a case where thereceiver device lets the transmitter device reset a contents protectionprocess while a signal level of the HPD line is a high level, andtransmitting, by the receiver device, a second CEC message to thetransmitter device, for enabling the transmitter device to read the EDIDof the receiver device and letting the transmitter device start aprocess of the contents protection while a signal level of the HPD lineis a high level, wherein the transmitter device does not read the EDIDof the receiver device after the transmitter device receives the firstCEC message, until the transmitter device receives the second CECmessage from the receiver device, and wherein the transmitter devicestarts the process of the contents protection after the transmitterdevice receives the second CEC message from the receiver device.